Pyrazole compounds having a hydroxyl group at the 3-position, such as 1-(4-chlorophenyl)-3-hydroxypyrazole, are useful as intermediates in the production of pharmaceuticals, etc., and an industrial production method therefore has been desired.
U.S. Pat. No. 6,040,458 discloses a production method including oxidizing 1-(4-chlorophenyl)pyrazolidin-3-one in water using oxygen in the presence of a base and a metal salt such as cobalt acetate.